第16周《C++语言基础》程序阅读——异常处理和命名空间

标签：c++   编程   namespace   

问题描述：

阅读下面的程序，写出输出结果

（1）

<code class="hljs cpp has-numbering"><strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;"><span class="hljs-preprocessor">#include <iostream ></span>
<span class="hljs-keyword">using</span> <span class="hljs-keyword">namespace</span> <span class="hljs-built_in">std</span>;
<span class="hljs-keyword">int</span> a[<span class="hljs-number">10</span>]= {<span class="hljs-number">1</span>,<span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>, <span class="hljs-number">8</span>, <span class="hljs-number">9</span>, <span class="hljs-number">10</span>};
<span class="hljs-keyword">int</span> fun( <span class="hljs-keyword">int</span> i);
<span class="hljs-keyword">int</span> main()
{
    <span class="hljs-keyword">int</span> i ,s=<span class="hljs-number">0</span>;
    <span class="hljs-keyword">for</span>( i=<span class="hljs-number">0</span>; i<=<span class="hljs-number">10</span>; i++)
    {
        <span class="hljs-keyword">try</span>
        {
            s=s+fun(i);
        }
        <span class="hljs-keyword">catch</span>(<span class="hljs-keyword">int</span>)
        {
            <span class="hljs-built_in">cout</span><<<span class="hljs-string">"数组下标越界!"</span><<endl;
        }
    }
    <span class="hljs-built_in">cout</span><<<span class="hljs-string">"s="</span><<s<<endl;
    <span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}
<span class="hljs-keyword">int</span> fun( <span class="hljs-keyword">int</span> i)
{
    <span class="hljs-keyword">if</span>(i>=<span class="hljs-number">10</span>)
        <span class="hljs-keyword">throw</span> i;
    <span class="hljs-keyword">return</span> a[i];
}</span></strong></code><ul style="FILTER:  ; ZOOM: 1" class="pre-numbering"><li><strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">1</span></strong></li></ul>

预计运行结果：

数组下标越界！

s=55

实际运行结果：

（2）

<code class="hljs cpp has-numbering"><strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;"><span class="hljs-preprocessor">#include <iostream></span>
<span class="hljs-keyword">using</span> <span class="hljs-keyword">namespace</span>  <span class="hljs-built_in">std</span>;
<span class="hljs-keyword">namespace</span> CounterNameSpace
{
<span class="hljs-keyword">int</span> upperbound;
<span class="hljs-keyword">int</span> lowerbound;

<span class="hljs-keyword">class</span> counter
{
    <span class="hljs-keyword">int</span> count;
<span class="hljs-keyword">public</span>:
    counter(<span class="hljs-keyword">int</span> n)
    {
        <span class="hljs-keyword">if</span> (n <= upperbound )
        {
            count = n;
        }
        <span class="hljs-keyword">else</span>
        {
            count = upperbound;
        }
    }

    <span class="hljs-keyword">void</span> reset(<span class="hljs-keyword">int</span> n)
    {
        <span class="hljs-keyword">if</span> (n < upperbound)
        {
            count = n;
        }
    }

    <span class="hljs-keyword">int</span> run()
    {
        <span class="hljs-keyword">if</span> (count > lowerbound)
        {
            <span class="hljs-keyword">return</span> count--;
        }
        <span class="hljs-keyword">else</span>
            <span class="hljs-keyword">return</span> lowerbound;
    }
};
}

<span class="hljs-keyword">int</span> main()
{
    CounterNameSpace::upperbound = <span class="hljs-number">100</span>;
    CounterNameSpace::lowerbound = <span class="hljs-number">0</span>;
    CounterNameSpace::counter ob1(<span class="hljs-number">10</span>);
<span class="hljs-keyword">int</span> i;

    <span class="hljs-keyword">do</span>
    {
        i = ob1.run();
        <span class="hljs-built_in">cout</span> << i << <span class="hljs-string">" "</span>;
    }
    <span class="hljs-keyword">while</span> (i > CounterNameSpace::lowerbound);
    <span class="hljs-built_in">cout</span> << endl;

    CounterNameSpace::counter ob2(<span class="hljs-number">20</span>);
    <span class="hljs-keyword">do</span>
    {
        i = ob2.run();
        <span class="hljs-built_in">cout</span> << i << <span class="hljs-string">" "</span>;
    }
    <span class="hljs-keyword">while</span> (i > CounterNameSpace::lowerbound);
    <span class="hljs-built_in">cout</span> << endl;

    ob2.reset(<span class="hljs-number">100</span>);
    <span class="hljs-keyword">do</span>
    {
        i = ob2.run();
        <span class="hljs-built_in">cout</span> << i << <span class="hljs-string">" "</span>;
    }
    <span class="hljs-keyword">while</span> (i > CounterNameSpace::lowerbound);
    <span class="hljs-built_in">cout</span> << endl;

    <span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}</span></strong></code><ul style="FILTER:  ; ZOOM: 1" class="pre-numbering"><li><strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">1</span></strong></li></ul>

预计运行结果：

10 9 8 7 6 5 4 3 2 1 0

20 19 18 17 16 15 14 13 12 11 

10 9 8 7 6 5 4 3 2 1 0

0

实际运行结果：

（3）将（2）中的main函数换作如下形式，其余不变

<code class="hljs cpp has-numbering"><strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;"><span class="hljs-keyword">int</span> main()
{
    <span class="hljs-keyword">using</span> CounterNameSpace::upperbound;
    upperbound = <span class="hljs-number">100</span>;   <span class="hljs-comment">//(a)</span>
    CounterNameSpace::lowerbound = <span class="hljs-number">0</span>;  <span class="hljs-comment">//(b)</span>
    CounterNameSpace::counter ob1(<span class="hljs-number">10</span>);
    <span class="hljs-keyword">int</span> i;
    <span class="hljs-keyword">do</span>
    {
        i = ob1.run();
        <span class="hljs-built_in">cout</span> << i<<<span class="hljs-string">" "</span>;
    }
    <span class="hljs-keyword">while</span>( i > CounterNameSpace::lowerbound);
    <span class="hljs-built_in">cout</span> << endl;

    <span class="hljs-keyword">using</span> <span class="hljs-keyword">namespace</span> CounterNameSpace;
    counter ob2(<span class="hljs-number">20</span>);
    <span class="hljs-keyword">do</span>
    {
        i = ob2.run();
        <span class="hljs-built_in">cout</span> << i<<<span class="hljs-string">" "</span>;
    }
    <span class="hljs-keyword">while</span>( i > CounterNameSpace::lowerbound); <span class="hljs-comment">//(c)</span>
    <span class="hljs-built_in">cout</span> << endl;

    ob2.reset(<span class="hljs-number">100</span>);
    lowerbound = <span class="hljs-number">90</span>;   <span class="hljs-comment">//(d)</span>
    <span class="hljs-keyword">do</span>
    {
        i = ob2.run();
        <span class="hljs-built_in">cout</span> << i <<<span class="hljs-string">" "</span>;
    }
    <span class="hljs-keyword">while</span>( i > lowerbound);  

    <span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}</span></strong></code><ul style="FILTER:  ; ZOOM: 1" class="pre-numbering"><li><strong><span style="font-family:KaiTi_GB2312;font-size:18px;color:#ff6666;">1</span></strong></li></ul>

预计运行结果：

10 9 8 7 6 5 4 3 2 1 0

20 19 18 17 16 15 14 13 12 11 

10 9 8 7 6 5 4 3 2 1 0

90

实际运行结果：

请回答：
(a)(d)处：为什么可以省去CounterNameSpace::？ 

因为之前使用过了！
(b)(c)处：是否可以省去CounterNameSpace::？

能！

第16周《C++语言基础》程序阅读——异常处理和命名空间

标签：c++   编程   namespace   

原文地址：http://blog.csdn.net/zp___waj/article/details/46560311